Chemistry is an essential science for understanding and developing construction materials. Specifically, the application of the green chemistry concept to the cement sector may allow the fabrication of new environmentally friendly materials with good sustainability and energy efficiency. Cellular concretes are an excellent alternative to conventional concrete in terms of thermal insulation and material economy. In this paper, the development of waste-based cellular concrete is presented; due to its good performance and low environmental impact, this focus is warranted. Three different cellular concrete systems were investigated: (i) traditional cellular concrete based on ordinary Portland cement and commercial aluminium powder; (ii) geopolymer cellular concrete applying alkali-activated chemical technology with a comparison of the use of two precursors, fluid catalytic cracking catalyst residue (FCC) and blast furnace slag (BFS), and recycled aluminium foil as an aerating agent; (iii) eco-cellular concrete, where commercial waterglass was replaced by an agro-industrial by-product, rice husk ash (RHA), in the activating solution. The development of geopolymer cellular concretes with different precursors and activating solutions has proven that the production of this type of concrete using different types of precursors is possible, depending on the availability of by-products and wastes. The densities, compressive strengths, and thermal properties of the three cellular concrete systems are assessed and a complete study on the carbon footprints of the developed concretes is presented. The results show that the alternative concretes have densities from 474 to 813 kg m⁻³, with compressive strengths from 2.6 to 4.6 MPa and thermal conductivities from 0.083 to 0.281 W m⁻¹ K⁻¹. In the case of the cellular concrete prepared using RHA in the activating reagent, the heat released from the dissolution of NaOH pellets in water dissolved the soluble silica present in the ash. This production method resulted in a reduction of its carbon footprint by 78%.

Rice husk ash is one of the most widely studied biomass ashes used in pozzolanic addition. Given its lower silica content, rice straw ash (RSA) has been explored less often, despite the fact that, according to the United Nations Food and Agriculture Organization (FAO), rice straw (RS) production is estimated at 600 million tons/year. In this work, RSA was physically and chemically characterized, and its pozzolanic properties were assessed. A controlled conditioning, burning, homogenization and grinding procedure was carried out to obtain RSA from RS. Chemical composition, insoluble residue, reactive silica, chloride content and particle size distribution were assessed for ash characterization. To determine RSA pozzolanicity, Frattini, electrical conductivity and pH measurements in an aqueous suspension of hydrated CH/RSA mixtures were obtained. Portland cement (PC) mortars with 15% and 30% RSA substitutions evaluated. The mechanical tests showed specimens with a strength activity index up to 90% and 80% with 15% and 30% RSA, respectively, after 3 days, and these values grew to 107–109% after 90 curing days.

Soil stabilization using cementing materials is a well-known procedure for earth-based building blocks preparation. For the selected binding materials, innovation usually focuses on low carbon systems, many of which are based on alkaline activation. In the present paper, blast furnace slag (BFS) is used as a mineral precursor, and the innovative alkali activator was olive stone biomass ash (OBA). This means that the most important component in CO₂ emissions terms, which is the alkali activator, has been replaced with a greener alternative: OBA. The OBA/BFS mixture was used to prepare compacted dolomitic soil blocks. These specimens were mechanically characterized by compression, and water strength coefficient and water absorption were assessed. The microstructure of blocks and the formation of cementing hydrates were analyzed by field emission scanning electron microscopy and thermogravimetry, respectively. The final compressive strength of the 120-day cured blocks was 27.8 MPa. It was concluded that OBA is a sustainable alkali activator alternative for producing BFS-stabilized soil-compacted blocks: CO₂ emissions were 3.3 kgCO₂/ton of stabilized soil, which is 96% less than that for ordinary Portland cement (OPC) stabilization.

Worldwide cement production is around 4.2 billion tons, and the fabrication of one ton of ordinary Portland cement emits around 900 kg of CO₂. Blast furnace slag (BFS) is a byproduct used to produce alkali-activated materials (AAM). BFS production was estimated at about 350 million tons in 2018, and the BFS reuse rate in construction materials of developing countries is low. AAM can reduce CO₂ emissions in relation to Portland cement materials: Its use in construction would be a golden opportunity for developing countries in forthcoming decades. The present research aims to formulate AAM destined for future applications in developing countries. Two activators were used: NaOH, Na₂CO₃, and a mixture of both. The results showed that compressive strengths within the 42–56 MPa range after 28 curing days were obtained for the Na₂CO₃-activated mortars. The characterization analysis confirmed the presence of hydrotalcite, carbonated phases, CSH and CASH. The economic study showed that Na₂CO₃ was the cheapest activator in terms of the relative cost per ton and MPa of manufactured mortars. Finally, the environmental benefits of mortars based on this reagent were evidenced, and, in terms of kgCO₂ emissions per ton and MPa, the mortars with Na₂CO₃ yielded 50% lower values than with NaOH.